Controller for relay

ABSTRACT

A relay control circuit enables releasing of welding of contacts in a short period by applying an bombardment pulse effective for welded contacts of the relay. Welded contacts of a relay are detected and subsequently input a signal to a microcomputer. A first driver is connected to an output port of the microcomputer which controls the relay, and a second driver is provided to another output port for driving the relay in parallel. This configuration allows to drive the first and second drivers alternately when contacts of the relay are welded, in order to apply an effective bombardment pulse for ensuring rapid separation of the welded contacts.

This application is a U.S. national phase application of PCTinternational application PCT/JP98/03995.

FIELD OF THE INVENTION

The present invention relates to the field of relay control circuitsemployed for driving and controlling relays using microcomputers.

BACKGROUND OF THE INVENTION

One known technology for controlling relays and releasing weldedcontacts autonomously using a microcomputer is configured as shown inFIG. 6. More specifically, reference numeral 21 is a microcomputer,reference numeral 21a is a +DC power supply VDD, and reference numeral21b is a power supply VSS on a common line with the load power supply. Arelay 22 is connected to a relay control output 21c of the microcomputer21 through a driver transistor 23. A contact 24a of the relay 22 isconnected to a power supply 26 through a load 25, and another contact24b is connected to an input 21d of the microcomputer 21 to detectwelding of the contact 24a.

Control operations when the contact is welded in the above configurationis briefly described below.

When the relay control output 21c of the microcomputer 21 switches fromON to OFF, the coil voltage of the relay 22 turns OFF, and the load 25also turns OFF. At this point, if the relay 24a is welded, the contact24a remains turned ON and the recovery signal from the contact 24b fordetecting welded contacts will not return to the input 21d of themicrocomputer 21, thus generating the message that welding has occurred.This switches the control signal from the relay control output 21c ofthe microcomputer 21 to the welded contact release mode, in which ashort pulse signal is applied to the coil of the relay 22 to release thewelded contacts. If the contacts separate immediately, the weldingreleasing mode returns to the normal control mode. If not, the weldingreleasing operation is repeated until the contact is released.

With the above conventional configuration, however, a rise time istypically required by the relay driving power supply before a subsequentpulse can be applied to release the welded contacts. This causes a lackof continuity in the release pulse, decreasing its effectiveness.

Moreover, if an instantaneous power failure occurs during normaloperation of the relay and the driving power supply of the relay isregained without reaching a sufficient sensory voltage level, the relaycontacts may remain turned off, or contact pressure may becomeinsufficient. In the worst case, the contact may generate heat,resulting in degradation of the reliability of the entire piece ofequipment.

SUMMARY OF THE INVENTION

A relay control circuit controls the load at a contact of the relay. Therelay control circuit comprises a microcomputer for controlling therelay, a welded-contact detector for detecting welded contacts in therelay and subsequently inputting a signal to the microcomputer, andfirst and second drivers for switching the relay control signal of themicrocomputer, in response to the signal from the contact weldingdetector, to a short pulse signal if the contact is welded. The firstand second drivers are employed to drive the relay in parallel.

Using this configuration, if welding of the contact occurs, anbombardment pulse effective in releasing the contact can be applied bydriving the relay in parallel, thus enabling rapid release of the weldedcontacts. When a recovery problem of the contact occurs due toinsufficient rise of driving power, the contact can be recovered bysupplying the relay driving signal from another output port provided inparallel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram showing a configuration of a control circuitof a relay in accordance with a preferred embodiment of the presentinvention.

FIG. 2 is a timing chart illustrating effect at occurrence ofinstantaneous power failure in accordance with the preferred embodiment.

FIG. 3 is a timing chart illustrating a welding release control patternin accordance with the preferred embodiment.

FIG. 4 is a timing chart illustrating another welding release control inaccordance with the preferred embodiment.

FIG. 5(a) is an enlarged view of the relay in accordance with thepreferred embodiment.

FIG. 5(b) is an enlarged section view illustrating a contact conditionof the relay.

FIG. 6 is a control circuit diagram of a relay employing a conventionalwelding releasing method.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention is described next withreference to drawings.

FIG. 1 is a circuit diagram of a relay control circuit in a preferredembodiment of the present invention.

In FIG. 1, reference numeral 1 is a microcomputer, reference numeral 2is a relay, and reference numeral 6 is a first driver which comprises atransistor 3, rectifying diode 4, and smoothing capacitor 5. Referencenumeral 7 is a second driver which comprises a transistor 8, rectifyingdiode 9, and smoothing capacitor 10. Each base of the transistors 3 and8 are respectively connected to the output ports 1a and 1b of themicrocomputer 1. Each collector of the transistors 3 and 8 are connectedin parallel to the relay 2.

Reference numeral 11 is a constant voltage element for securing voltagewhen driving the relay, and reference numeral 12 is a current limitingresistance for the constant voltage element, which also functions as aholding current limiting resistance for suppressing coil temperaturerise during operation of the relay. Reference numeral 14 is a commercialpower supply to which a load 13 is connected via contacts 2a and 2b ofthe relay. A contact 2c is used for detecting welding of the contacts 2aand 2b, and is connected to the input port 1c of the microcomputer 1.

The operation of the preferred embodiment is described next withreference to FIG. 1.

When a relay driving signal is output from the output port 1a of themicrocomputer 1, the transistor 3 turns ON to apply the DC voltagecharged to the smoothing capacitor 5 to the relay 2, and the relay 2 isdriven. Accordingly, the contacts 2a and 2b of the relay are turned ON,and the current flows through the load 13. When the relay driving signalfrom the output port 1a of the microcomputer 1 is turned OFF, the inputport 1c of the microcomputer 1 detects the signal indicating recovery ofthe contact 2b to the contact 2c of the relay.

If the contacts are welded and the recovery signal is not detectable,the output port 1a switches to output a short pulse signal from thefirst driver 6 to apply bombardment on the welded contacts. In addition,after applying a pulse from the first driver 6, a short pulse signalfrom the output port 1b of the microcomputer 1 is immediately applied bythe second driver 7. Consecutive strong bombardment pulses from theseoutput ports 1a and 1b continue until the welded contacts separate. Oncethe welded contacts have separated, the recovery level is regained atthe contact 2c, and the input port 1c of the microcomputer 1 receives asignal indicating that the welded contacts have separated. The shortpulse signal from the output port 1a is then switched to a normaloperation signal. The output port 1b stops outputting signals, andnothing further is executed during normal operation except for thefollowing operations.

Other operations in this preferred embodiment shown in FIG. 1 aredescribed with reference to FIG. 2.

The operations which follow when instantaneous power failure of thecommercial power supply occurs in the circuit diagram shown in FIG. 1are described with reference to FIG. 2. If the commercial power supply14 is applied at Point a, the DC power supply of the microcomputer 1 issupplied at approximately the same time. The driving power supply of therelay 2, as described above, drives the relay 2 using the voltagecharged in the smoothing capacitor, suppressing any temperature rise ofthe coil of the relay 2. After it is activated, the driving current ismaintained at the minimum required holding current by limiting thedriving current by means of the current limiting resistance 12.

Accordingly, the voltage of the first driver 6 of the relay 2 settles toa predetermined level at Point b, slightly later than the point of theinput power supply, depending on the time constant of the smoothingcapacitor 5 and the resistance 12. In general, the time involved isshorter than a few seconds, showing no problem in practical use. In thesame way, the voltage of the second driver 7 settles to a predeterminedlevel at Point c. When the control signal of the relay 2 is output fromthe output port 1a of the microcomputer 1 at Point d, the high voltageat Point e stored in the smoothing capacitor 5 at Point e is applied tothe relay 2. When the contacts of the relay 2 close at Point f, the coilcurrent of the relay 2 levels out at the minimum required holdingcurrent at Point g.

If instantaneous power failure suddenly occurs at Point h, the voltagelevel of the first driver 6 drops, reducing the coil current to belowthe holding voltage at Point i. In this case, the contacts of the relay2 open at Point j. Even if the power failure is recovered at Point k,the control signal from the output port 1a of the microcomputer 1remains ON. Accordingly, the voltage for restarting the relay 2 cannotbe expected to match that at Point (1). The contact of the relay 2remains open as shown by Point (2), which means the load cannot bedriven. Even if the contact point is closed, sufficient contact pressurecannot be secured due to reasons such as heat generation at the contact,which may degrade reliability. Therefore, after power is regained, thecontrol signal for the second driver 7 is output at Point m from theoutput port 1b of the microcomputer 1 so that the relay 2 gains a highcoil current at Point n, making the contact return to its normal stateat Point o.

The control circuit of the relay 2 as operated above enables the rapidrelease of welded contacts by applying an effective bombardment pulseusing more than one driving circuit when the contacts are welded. At thesame time, the contact can be recovered by supplying the driving signalfrom another parallel output port even if there is a problem withrecovery of the relay due to insufficient rise of driving power.Accordingly, the present invention has the advantageous effect ofproviding a relay control circuit that solves all these problems at thesame time.

Next, the operation of parallel driving based on more than one controlpattern programmed by the microcomputer is described with reference toFIG. 3.

FIG. 3 illustrates the control pattern output from the output ports 1aand 1b when the input port 1c of the microcomputer detects a weldedcontact. The control signal for the relay 2, switched to a short pulsesignal (approximately 500 ms), is output from the output port 1a atPoint A. When this pulse signal is cut off at Point B, a control signalis output from the output port 1b at Point C, allowing time to turn OFFthe contact of the relay 2. The same operations are repeated at points Dand E until the welded contacts are separated. This is the basic mode ofoperation.

Next, in the pressure mode, a slightly longer pulse (500 ms to 1 s) isoutput at Point F, and then cut off at Point G. Then, as describedabove, a short pulse is output from the output port 1b at Point H,providing sufficient time to turn OFF the contact of the relay 2. Thesame operations are repeated at Points I and J until the welded contactsare separated.

In the bombardment mode, an extremely short pulse (200 ms maximum) isoutput from the output port 1a at Point K. The extremely short pulse isalso output from the output port 1b at Point L, allowing sufficient timeto turn OFF the contact of the relay 2. The same operations are repeatedat Points M and N until the welded contacts are separated.

The above three modes can be executed independently, combined, orcombined and rearranged. A wide range of applications are achievable bycreating programs that gain the most effective results.

As described above, by alternately driving the first driver and seconddriver for the control signal of the relay based on more than onecontrol pattern programmed by the microcomputer, an bombardment pulseeffective in separating the welded contacts is applied in a shortperiod, ensuring the effect of releasing the welded contacts. At thesame time, the inching operation, which was conventionally thought to beproblematic, becomes feasible.

Furthermore, other effects are achievable by creating a program as shownin FIG. 4, which is described next.

In FIG. 4, if the driving signal for the relay is input at Point A, thefirst driver 6 and second driver 7 are activated at almost the sametime. The contact of the relay coil closes vigorously in the initialperiod (A to B) in the contact transfer section E as a result of thesecond driver 7 applying the maximum voltage for driving the relay.Then, after Point B, the relatively low voltage of the first driver 6 isapplied during the rest of the contact operation section, and theoperation then proceeds to the contact closing section (C to D).

This series of operations in the starting mode achieves two effects. Oneis to suppress deviations in the operating period as a result ofmechanical friction at starting operation. This is achieved by forciblydriving the contact with the second driver 7 during the contact transfersection E (A to C). Accordingly, the above operation is an effectivemeans for reducing repeated deviations.

Another effect is the suppression of mechanical bombardment noise whenclosing the contact by driving in the low-voltage mode, using theminimum required voltage, between the last part (B to C) of the contacttransfer section E and the contact closing section F. Accordingly, theabove operation is an effective means for reducing relay noise. Inaddition, by outputting the relay driving signal G from the seconddriver 7 after completing the contact closing section F, the adsorptionpower of the coil can be reinforced to secure full contact pressure evenif it is insufficient when closing the contact. The relation of thedriving period of the first driver 6 and the second driver 7 can beexpressed using the following formula:

E×k>H

in which

E=Time of the contact transfer section

k=Coefficient of 0.1 to 0.9

H=Operating period of the second driver.

The following FIGS. 5(a) and 5(b) show a model of the state of a contactportion of the relay used in this preferred embodiment. In thesefigures, the reference numeral 2a is NO contact (fixed contact) and thereference numeral 2b is COM contact (movable contact). A film (2d) suchas an oxidized or contaminated film is adhered to the surface of thesecontacts. As illustrated in the Figures, more than one metalmicro-protrusion contact each other just by their tips (arrow A) whenthe current flows. Thus a current flow route is formed.

Accordingly, in the preferred embodiment, if the first driver is drivenby a voltage lower than the rated voltage of the relay within thecontrollable range of the relay, the area of melted and welded portionscan be minimized if contact welding occurs for any reason. Extension ofmicro-protrusions on the contact surface can also be minimized. Thissuppresses to minor welding, and even prevents occurrence of minorwelding. In addition, the bouncing phenomenon that occurs when thecontact is turned ON can be minimized by applying low voltage, resultingin a marked extension of the service life of the contact.

It should be noted that the capability for autonomously releasing thewelded contacts decline at lower driving voltages. In other words, theknocking pulse becomes weaker. However, a stronger bombardment can beapplied by setting the driving voltage of the second driver higher thanthat of the first driver (for example, greater than the rated voltagebut within the maximum rating), and driving the first and second driversin parallel. This also allows to secure sufficient autonomous releasingcapability.

Industrial Applicability

As described above, a relay control circuit the application of anbombardment pulse effective in separating the welded contacts by drivingthe relay in parallel. This achieves rapid release of the weldedcontacts. The contact can also be recovered by supplying the drivingsignal to the relay from another output port provided in parallel evenif problems arise with recovery of the relay due to insufficient rise ofthe driving power supply.

Moreover, the most effective bombardment pulse can be applied byalternately driving the first driver and second driver, which is todrive the relay in parallel, based on more than one control patternprogrammed into the microcomputer.

Furthermore, since the first driver is driven at a lower than ratedvoltage, if any welding does occur, it will be minor. Extension ofmicro-protrusions on the contact surface can be prevented because littlebouncing takes place when the contact is turned ON. This significantlyextends the service life of the contact, and enables the application ofa strong bombardment on the welded portion, since the second driver isdriven at a voltage larger than the rating if contact welding occurs.

Furthermore, the second driver is forcibly but temporarily operated atthe maximum driving voltage of the relay in the starting mode tosuppress deviations at startup as a result of mechanical friction duringthe initial period of operation of the relay. This reduces deviations inrepeated operation time. Then, the contact is closed by the first driverat the minimum driving voltage required, achieving the advantageouseffect of reducing the noise level during relay operation.

Although illustrated and described herein with reference to certainspecific embodiments, the present invention is nevertheless not intendedto be limited to the details shown. Rather, various modifications may bemade in the details within the scope and range of equivalents of theclaims and without departing from the spirit of the invention.

What is claimed is:
 1. A relay control circuit for controlling load atcontacts of a relay, comprising:a microcomputer for controlling saidrelay; a welded contact detector for detecting that said contacts arewelded, and for subsequently inputting a signal to said microcomputer;and first and second drivers for switching a relay control signal ofsaid microcomputer from a normal signal to provide a short pulse signalat said welded contacts based on said signal from said welded contactdetector; wherein said first and second drivers are coupled in parallelfor driving said relay.
 2. The relay control circuit as defined in claim1, wherein driving voltages of said first and second drivers aredifferent.
 3. The relay control circuit as defined in claim 1, whereinsaid first and second drivers are controlled with a different controlpattern respectively to drive the relay in parallel at said weldedcontacts, each of said control patterns programmed in the microcomputer.4. The relay control circuit as defined in claim 1, wherein said firstdriver is driven at a voltage smaller than the rating of the relay, andsaid second driver is driven at a voltage greater than the rating ofsaid relay but within the maximum rating.
 5. The relay control circuitas defined in claim 1, wherein said second driver is forcibly driventemporarily at approximately the maximum driving voltage of the relay atstartup, and then said first driver is driven at a minimum requiredvoltage.
 6. The relay control circuit as defined in claim 1, whereinsaid first driver is controlled with a control pattern continuously andsaid second driver is controlled with a control pattern intermittently.